Electronic devices—such as integrated circuits (for example, non-volatile memories)—are generally subject to a functional test to verify their correct operation; this may be of the utmost importance to ensure a high quality of a production process of the electronic devices. For such purpose, some electronic devices are provided with a BIST (Built-In Self Test) machine being implemented within the electronic device; such BIST machine is capable of self-performing the functional test of the electronic device and outputting its result.
Furthermore, the functional test may be supported by a conditioning procedure, which subjects the electronic devices to be tested to stress conditions for simulating a long period of operation in standard conditions; in such way, the functional test being performed by the BIST machine on an electronic device subject to the conditioning procedure implements a reliability test, which is used for identifying potential defects in the electronic device (that is, that may occur after a certain period of use).
The conditioning procedure of the electronic devices may be of thermal type, as in the case of a burn-in reliability test, which consists of having the electronic devices operate at very high or very low temperatures (for example, from −50° C. to +150° C.); otherwise, the conditioning procedure of the electronic devices may be of both thermal and voltage type, as in the case of an OLT (Operating Life Test) reliability test.
In general, the reliability test is performed by having the electronic devices operate continuously (for example, for about 1,000 hours) in a conditioning machine that subjects the electronic devices to variable conditions of temperature and/or voltage (for example, by causing the functional test to be executed cyclically by their BIST machines without detecting the result). At the end of such conditioning procedure, the electronic devices are provided to a verification machine in which they are again subject to the same functional test (being performed by their BIST machines), in order to detect the defective electronic devices.
However, such reliability test may have some drawbacks that preclude its use on a large scale.
First of all, in the present state of the art, defective electronic devices may be identified only at the end of the reliability test (in the verification machine), because the conditioning machine may be incapable of detecting the results provided by the BIST machines. However, in this way no information is available about the particular temperature conditions and/or voltage conditions wherein each defect manifested itself (in the conditioning machine).
Moreover, the power consumption of the electronic devices may not be minimized, substantially for two reasons. Firstly, at the end of the conditioning procedure it may be necessary to perform an additional functional test by the BIST machines, with consequent waste of electric power (as well as time). Secondly, since each BIST machine performs the functional test on all the chips included in the corresponding electronic device indiscriminately for the whole (long) duration of the conditioning process, there may also be a waste of processing power, since all the integrated circuits are typically always tested (including the ones being already detected as defective in a previous functional test).